Mesoscale modeling of biological fluids: from micro-swimmers to intracellular transport

Sayed Iman Mousavi, Worcester Polytechnic Institute

Abstract

After more than a century, there are no analytical solutions for the Navier-Stokes equations to describe complex fluid behavior, and we often resort to different computational methods to find solutions under specific conditions. In particular, to address many biological questions, we need to use techniques which are accurate at the mesoscale regime and computationally efficient, since atomistic simulations are still incredibly computationally costly, and continuum methods based on Navier-Stokes present challenges with complicated moving boundaries, in the presence of fluctuations. Here, we use a novel particle-based coarse-grained method, known as MPCD, to study ciliated swimmers. Using experimentally measured beating patterns, we show how we recapitulate the emergence of metachronal waves (MCW) on planar surfaces, and present new results on curved surfaces. To quantitatively study these waves, we also analyzed their effect on beating intervals, energy fluctuations, and fluid motion. We then extended our model to realistic cellular geometries, using experimentally obtained Basal Bodies locations.\par In the second part of our study, we focused on the intracellular fluid motion, neglecting hydrodynamic interactions. We developed the Digital Confocal Microscopy Suite (DCMS) that can run on multiple platforms using GPUs and can input realistic cell shapes and optical properties of the confocal microscope. It has this ability to simulate both (Fluorescence Recovery After Photobleaching) FRAP and Fluorescence Correlation Spectroscopy (FCS) experiments, as well as the capability to model photo-switching of fluorophores, acquisition photo-bleaching, and reaction-diffusion systems. With this platform, in collaboration with the Vidali Lab, we were able to elucidate the role of boundaries in interpreting FRAP experiments in \textit{moss} and estimate the binding rates of myosin XI.